Organic contaminants are a major problem in the pulp and paper-making industry. These contaminants accumulate during the paper-making process and deposit on both the process machinery and the final paper products. These deposits foul equipment, reduce the efficiency of the process, lower final product quality, and increase equipment maintenance costs including increased costs due to machine down-time, and reduce productivity. Increasingly, industry practice is to use closed mill water systems and recycled wood fiber, both of which increase the concentration of contaminants in the system.
Organic contaminants, such as hydrophobic pitch and stickies, can come from virgin or recycled pulp sources. The contaminants from virgin pulp include those naturally occurring tacky components of wood resins. Some hydrolyzed wood resins generate fatty acids that interact with the calcium present in water to form calcium soaps that are a main source of organic deposits. The contaminants from recycled pulp come from contaminants in recycled process water and from various sources in recycled wood pulp including, styrene-butadiene latex and poly(vinyl acetate) adhesives from paper-coatings, urethane-based adhesives, polyethylene from plastic film, and wax from hot melt adhesives. Hydrolyzed alkyl ketene dimer and alkenyl succinic anhydride may also cause deposits. Most tacky materials that form deposits are hydrophobic in nature and are either anionic or nonionic.
Dispersion and stabilization of tacky particles using dispersants is a common treatment technique used to remove contaminants in papermaking process. Dispersants such as talc, Kaolin clay, anionic dispersants, and nonionic poly(vinyl alcohol) are commonly used in the industry (U.S. Pat. No. 4,871,424). Surfactants, anionic polymers, and combinations of hydrophobic and anionic copolymers are also used extensively to prevent calcium soap deposits (James P. Casey, Pulp and Paper, Vol. II, 2nd Ed., pp. 1096-7). Earlier techniques used for the treatments of stickies included using organic solvents, such as propane, dioxins, chlorinated organic compounds, and supercritical carbon dioxide, to disperse and extract the stickies from wood pulp (U.S. Pat. No. 6,183,521).
Conventional dispersants may be ineffective in closed mill water systems because of contaminant build-up in the water requiring a process machine shutdown to clean the machinery and mill water. Cationic polymers and copolymers, alone or in combination, address this problem by fixing anionic contaminants onto pulp fibers. Various cationic polymers have been disclosed. For example, polydiallyl dimethylammonium chloride polymers (polyDADMAC) and copolymers are often used commercially. U.S. Pat. No. 5,393,380 discloses a poly(DADMAC) copolymer mixture of polydiallyl dimethylammonium chloride and 3-acrylamido-3-methylbutanoic acid used for contaminant control. Canadian Patent No. 1,150,914 discloses a group of cationic contaminant control polymers formed by reacting epichlorohydrin and dimethylamine.
Cationic polymers may be combined with other polymers or chemicals for the uses in papermaking process. U.S. Pat. Nos. 3,893,885 and 4,250,299 disclose a method of combining low molecular weight polyethyleneimine (PEI) with different cationic polymers for contaminant control. U.S. Pat. No. 5,300,194 discloses using PEI or quaternized cationic polymers together with an anionic polymer to control pitch or stickies deposits. U.S. Pat. Nos. 6,517,682 and 4,995,944 disclose methods for the deposit control using combinations of cationic polymers with one or more nonionic surfactants having a hydrophilic/lipophilic balance (HLB) of 11 to 14. Various other cationic polymers were disclosed for pitch deposition control, including dicyandiamide-formaldehyde (U.S. Pat. No. 3,582,461), quaternized polyamine ionene polymers (U.S. Pat. No. 4,765,867), and a copolymer composition of N,N-diallyl-N,N-dimethylammonium chloride with 3-acrylamido-3-methylbutanoic acid (U.S. Pat. No. 5,393,380). Some natural polymers can also be used for contaminant control. U.S. Pat. No. 5,885,419 discloses the use of blood-related proteins, such as albumin and globulins, for preventing pitch and stickies deposition.
Cationic polymers can be ineffective for removing hydrophobic nonionic stickies. Instead, a combination of cationic polymers and anionic surfactants or surface active compounds may be used. U.S. Pat. No. 6,977,027 discloses a stickies control additive for recycled pulp comprising talc particles treated with a tertiary or quaternary amine. U.S. Pat. No. 6,527,915 discloses a method for stickies control in papermaking process using a combination of surface active whey proteins and cationic polymers such as polydiallyl dimethylammonium.
Finally, single component chemicals, such as hydrophobically modified cationic polymers, may be used to control stickies. These polymers can fix anionic stickies and disperse nonionic hydrophobic stickies. U.S. Pat. No. 5,246,547 discloses a hydrophobic polyelectrolyte copolymer of polydiallyl dimethylammonium for contaminant control.
Poly(aminoamides) based cationic polymers are also known to the pulp and paper industry, but have not been used specifically to treat process water in papermaking to reduce or control contaminants. U.S. Pat. Nos. 4,407,994, 3,988,280, and 3,992,345 disclose water insoluble hydrophobically modified poly(aminoamides) polymers for paper sizing. These polymers cannot effective control contaminants in the pulp or in a papermaking process because the materials are not soluble or dispersible in water.